In recent years, integrated circuits have shown growing increases in their packing densities and in the production of semiconductor boards, such as VLSI, a process of forming ultra fine patterns having line widths of half micron or below has required. In order to meet such a requirement, wavelengths used in exposure apparatus for photolithography have become shorter and shorter, and now the use of excimer laser light (such as XeCl, KrF or ArF), namely light of shorter wavelengths in the far ultraviolet region, comes to be examined.
For pattern formation by photolithography in such a wavelength region, chemical amplification resists are usable.
Chemical-amplification resists are broadly classified into three groups known as a two-component system, a two-and-half-component system and a three-component system. The two-component system combines a compound capable of generating an acid when decomposed by light (a photo-acid generator) with a binder resin. The binder resin used in this system is a resin containing groups capable of decomposing under action of an acid and increasing resin's solubility in an alkali developer (acid-decomposable groups). The two-and-half-component system further contains a low-molecular-weight compound having an acid-decomposable group in addition to the photo-acid generator and the binder resin of the two-component system. The three-component system contains a photo-acid generator, an alkali-soluble resin, and a low-molecular-weight compound having an acid-decomposable group.
Although the chemical amplification resists are suitable as photoresists intended for ultraviolet or far ultraviolet irradiation, it is necessary for them to further support characteristics required from a working viewpoint.
As to photoresist compositions used in combination with an ArF light source, there is a proposal to introduce alicyclic hydrocarbon moieties into resins of the compositions for the purpose of imparting dry etching resistance. However, the introduction of alicyclic hydrocarbon moieties has a detrimental effect that the photoresist system becomes highly hydrophobic and difficult to dissolve in an aqueous tetramethylammonium hydroxide (TMAH) solution, or causes an undesirable phenomenon that the resist comes off the substrate during development.
With the intention of adapting to hydrophobicity of resins, measures of mixing organic solvents, such as isopropyl alcohol, in developers have been examined and made a fair success. However, those measures raise a concern about swelling of resist coatings and make processes complicated, and so it cannot always be said that they have resolved the problems. In approaches to improving resists, measures of introducing hydrophilic groups have often been taken to compensate for hydrophobicity of various alicyclic hydrocarbon moieties.
On the other hand, Japanese Patent Laid-Open No. 109632/1999 describes application of resins having polar group-containing alicyclic functional groups in addition to acid-decomposable groups in radiation-sensitive materials. And Japanese Patent No. 3042618 discloses the photoresist composition containing a polymer prepared by copolymerizing a (meth) acrylate derivative having a lactone structure and other polymerizable compounds.
As mentioned above, resins containing acid-decomposable groups, which are used in photoresists intended for exposure to far ultraviolet light, generally contain alicyclic hydrocarbon groups also in each individual molecule. Therefore, the resins become hydrophobic, and troubles arising therefrom are present. Although various measures to remedy such troubles have been examined, the arts as recited above still have many unsatisfactory points and improvements thereon are expected.
Further, Japanese Patent Laid-Open No. 2001-109154 discloses the positive photoresist composition containing a copolymer resin of alicyclic lactone and monohydroxyadamantane monomers, and thereby having high sensitivity, high resolution and improvement in pattern edge roughness. However, such a composition cannot provide sufficient improvements in a pattern topple problem and a surface roughening trouble upon etching. The term “pattern topple” as used herein means a phenomenon that, when line patterns are formed, they topple onto a substrate as they snap in the vicinity of their interface with the substrate.
In addition, Japanese Patent Laid-Open Nos. 2000-338674 and 2001-183836 disclose the resist compositions containing copolymer resins of dihydroxyadamantane monomers and acid-decomposable adamantane monomers. However, those compositions are also insufficient to effect improvements in pattern topple, surface roughening upon etching, edge roughness and pitch dependency.